1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor laser element wherein a semiconductor laminated structure having an active layer is etched to form a mesa, and the circumference of the mesa is buried with a burying layer.
2. Background Art
In a semiconductor laser element, the current pathway must be narrowed to efficiently supply a current to the active layer. Therefore, in many semiconductor lasers, after fabricating a semiconductor laminated structure having an active layer, a mesa is formed using a technique to transfer micro-patterns to an insulative film and an etching technique to limit the region where a current flows, and to narrow the current pathway. At this time, from the standpoint of the protection of the active layer exposed on the side of the mesa, heat dissipation, or the parasitic capacity of the element, a buried structure wherein the circumference of the mesa is buried with semiconductors is formed (e.g., refer to Japanese Patent Laid-Open No. 05-136526).
FIG. 10 is a sectional view showing a semiconductor laser element wherein the circumference of the mesa in a semiconductor laminated structure having an active layer is buried with a structure laminated by n-type semiconductor layer, p-type semiconductor layer, n-type semiconductor layer and p-type semiconductor layer. A mesa of a semiconductor laminated structure wherein a p-type InP clad layer 12, an AlGaInAs lower optical confinement layer 13, an AlGaInAs-MQW active layer 14, an n-type AlGaInAs upper optical confinement layer 15, and an n-type InP clad layer 16 are sequentially grown on a p-type InP substrate 11, is formed. The circumference of the mesa is buried with a p-type InP burying layer 17, an n-type InP current blocking layer 18, a p-type InP burying layer 19, and an n-type InP burying layer 20. Thereon, an n-type InP contact layer 21, an n-type InGaAs contact layer 22, and an n-type InP cap layer 23 are formed.
Here, the side of the mesa must be coated with the p-type InP burying layer 17. This is because if the n-type InP current blocking layer 18 contacts the mesa, a current flows from the mesa to the burying layers, and the current to the active layer 14 cannot be narrowed.
The growth of the p-type InP burying layer 17 on the side of the mesa is much influenced by the surface state and the shape of the side of the mesa, which becomes the burying boundary. For example, the mesa has various shapes depending on the etching method and conditions for forming the mesa, or semiconductor material composing the mesa, and an inversely tapered portion may be formed on the side of the mesa. Since crystals are not grown on the inversely tapered portion, the inversely tapered portion is not coated with the p-type InP burying layer 19 in the initial stage of burying growth, and growth so as to coat the inversely tapered portion begins after the portion below the inversely tapered portion has been completely buried.
Therefore, there was a problem wherein the n-type InP current blocking layer 18 contacted the mesa, and an invalid current pathway 24 wherein a current flowed from the mesa to the burying layers was formed as FIG. 11 shows. To prevent the formation of the invalid current pathway, the etching conditions had to be reviewed for each device structure or semiconductor material composing the mesa, so that the shape of the mesa most suited to the burying growth was obtained.
In addition, in the mesa composed of Al-containing semiconductor materials, the Al on the side of the mesa was oxidized when it was exposed to the atmosphere, causing the inhibition of burying growth, and defective burying, such as pitted growth, easily occurred. There was another problem wherein oxygen or impurities in the boundaries caused crystal defect, and in turn caused the deterioration of the semiconductor element. For these reasons, the burying growth of a mesa composed of Al-containing semiconductor materials was difficult.